Resin bonded abrasive sheet material



May 2, 1944. R. P. CARLTON 5TM.l

RESIN BONDED ABRASIVE SHEET MATERIAL Filed Jan. 27, 1934 Inf/enfans s E'ZCZQPMZ @rifonm Patented May 2, i944 eric Richard faul Carlton and Byron J. (takes, St. Paul, Minn. assignors to Minnesota Mining & Manufacturing Qcimpany, St. Paul, Minn., a

corporation of Delaware Application January 27, 1934, Serial No. 708,662

18 Claims.

Our present invention relates'in general to the treatment of material preferably in sheet form, and more particularly the treatment of mate rial for purposes of forming or attaining composite structures of which Well-known forms of abrasives, as what is commonly known as sandpaper, is an example.

In the patents known to use for the producttion of such articles, of which Patent No. granted December 8, 1925; No. 1,581,657, granted April 20, 1926, and Reissue No. 17,593, February 11, 1930, are examples, a stable waterproof and flexible abrasive article in the nature of sandpaper and the process of manufacturing the same is described.

Such treatment and resulting product, through satisfactory, entails considerable expense, by reason of the time consumed and the time the necessary equipment is in use for producing such articles on a large commercial basis.

It is therefore an object of our invention to provide an abrasive article comprising primarily, a iiexible backing material in the nature of a felted fabric, such as paper, or a Woven fabric, such as cloth, as the base for a grit or layer of abrasive particles, and including a binder with or without 4sizing coats of a material that is waterproof, stable, and results in a final article which is flexible and resists the action of fluids used in abrading operations, and of a character to maintain the bonding eiiect of the abrasive article effective in dry or wetabrading operations throughout the eiective abrading life of the abrasive article, and which effects considerable economy in the production and cost of the article, by reason of the speed with which the article may be produced. It is contemplated by our invention to provide an abrasive article in the nature of sandpaper,.including as a component thereof, either as a binder, sizing coat, back coat or grit sizing coat, a stable, flexible and waterproof` material which acts more efficiently than such components as previously known to use, so far as inertness, Waterproofness, iiexibility and efficiently in abraiding operations are concerned, and which entails consid erable economy in labor and cost of production.

It is further contemplated as an object of our invention to provide stable.` iiexible and waterproof materials and methods of their production, for purposes particularly valuable in the production of abrasive articles in the nature of sandpaper, wherein products characterized by inert ness ln the presence of liquids used in .abradingv operations, together with waterproofness and flexibility, are obtained.

In the practice of our invention, we have found that the resinous componentl of the binder material may be substituted in whole or in part by a phenol-aldehyde condensation resin, such as a phenol-formaldehyde resin, and that, as a result of such substitution the time required for the setting or hardening or the binder is materially reduced, thus permitting greater speeds of production. And in addition to this highly desirable economy of time We are able to improve the quality of the end product by the said substitution.

Furthermore, we have` found that by proper selection and treatment of the fatty-oil and phenol-formaldehyde resin we are able to induce a reaction and/or polymerization involving said ingredients, thereby obtaining a resinous material differing substantially from all similar materials known to us and possessing properties particularly desirable for our purposes.

In a convenient form, the fatty-oil is preferably China-wood oil and the resin constituent is a phenol-formaldehyde resin of the Bakelite type which is acetone and oil soluble and potentially reactive with fatty oils. The China-wood oil and the phenol-aldehyde resin are preliminarly treated to induce polymerization. This is accomplished by melting the resin in the fattyoil While the oil is receiving its heat treatment. The reaction and/or polymerization of the phenol-formaldehyde and the fatty-oil occurs at approximately 235 degrees C.; and when natural resins or the glyptal type of resins are to be incorporated into the bond in addition tothe phenol-aldehyde resin, the second resin is preferably added after the aforementioned reaction has been carried to completion. We have found that the presence of a natural resin retards the reaction to the degree that it is present within the limits of reacting resin to combine with an acidic cil or resinous material, and under certain conditions, may, if not totally, partially inhibit the reaction between the oil and the reactive phenol-aidehyde resin, it present. Driers do not appear to influence this reaction. How ever, we find it convenient to vadd Some drier after the heat treatment in order to accelerate the drying or hardening of any excess of the fatty oil which does not enter into direct combination with the phenol-aldehyde resin. The driers may be of the type referred to in the prior Okie patent; other driers such as the ma tallio resinates. particularly manganese resinate and/or tungete may be used.

The oil resin compound so prepared may have added thereto a suitable thinner in quantities dependent upon the use to be made of it, either for the binder coat or sizing coat, or dependent upon the condition of the backing material which may or may not have been previously waterproofed. By selecting the proper thinner or mixture of thinners, and by controlling the amount added to the oil-resin compound We are able to obtain any desired degree of penetration into the backing material from complete saturation to a surface coating or film of sufficient thickness to act as the binder coat for the grit or layer of abrasive particles. Thus we may add between and 50% of thinner tothe oil-resin compound described above.

The polymerized resin-oil and thinner composition may be used to saturate a backing material, surface coat the same, where the inherent nexibility of the backing material is desired retained, or be added to a previously treated paper to leave a substantial residuum serving as a binder coat for the grit or layer of abrasive particles. In use with' higher percentages of thinner, the compo= sition is preferably used for the grit sizing, in accordance with the process outlined in the Okie patents previously described.

A convenient formula for our purposes is as follows:

Thinners About 12.0

The percentages above given are by weight.

The thinner preferred by us is a hydrocarbon of the petroleum series, known on the market as oleum spirits, and has a boiling range of 125 to 244 degrees C.; initial boiling point not below 125 degrees C.; not more than 50% over at 171 degrees C.; recovery at least 95%; residue colorless; end point below 244 degrees C. To a certain extent, petroleum spirit of a boiling range between 60 and 120 degrees C.. specific gravity .67 to .70 may be used. Also varnish makers and painters naphtha may be used. This product has a boiling range of 100 to 160 degrees C.; specific gravity .73. White spirit may also be used, which is a petroleum hydrocarbon having a boiling range of 80% below 190 degrees C.; 90% below 200 degrees C. Lacquerpetro may also be used which is a hydrocarbon solvent of the petroleum series; 85% distilling below 200 degrees C.; 97% distilling below 220 degrees C.

Where the ratio of the resin to the oil is greater than 1-3, either turpentine or solvent naphtha (coal tar solvents) vmust be used as the major part of the thinners. Where the ratio is 1-3 or less, oleum spirits may be used.

Additionally, the thinner may be a mixture of turpentine and the hydrocarbon solvents above enumerated.

" As the resulting oil resin compound, as contemplated by us and above described, has certain oxidation properties indicating a portion of the drying oil to retain some of the drying characteristics, the thinner as contemplated by our invention is one which has solvent action upon the oilresin to retain a homogeneous mixture through all stages of separation of the thinner, in accordance with the further treatment to which the article is submitted in its production.

'I'he composition as prepared by our invention is applied to a backing material, either by surface coating or an impregnation, when a layer serving as the binder coat is applied. The grit or layer oi abrasive particles is incorporated in a surface coating upon the backing material, in accordance with processes heretofore devised for incorporating the same upon the web of fabric carrying the adhesive oil resin composition. This may be accomplished after a layer of the polymerized oil resin compound has been formed on the backing material, and before the thinner has been fully volatilized.

The backing, now carrying the polymerized oil resin composition and a grit or layer of abrasive particles, is passed to drying rooms, where the thinner is progressively removed. The drying action is continued in rooms in which the air is well circulated, preferably at elevated temperatures of aboutl20 to 150 degrees F.

The application of the materials in the web so prepared, forms a film which is dust free, that is, a lm to which dust will not readily adhere in fifteen minutes and can easily be handled in one hour.

The particular features of our invention thus far described, distinguishing from the waterproofing ingredients used in said prior Okie patents, reside in the production of a film which is equally flexible, but of tougher and harder characteristics. The film is substantially resistant to all liquids which may be used in abrading operations, such as water, oils, solutions of detergents and gasoline. The period for setting or drying the final product is materially reduced. As compared with artificial resins, such as phenol-formaldehyde condensation resins of the Bakelite type, our composition is productive of greater speeds of operation and produces a tougher, more flexible product, and for substantially thick binder coats without necessitating rigid backing forms, mold and/or pressure to react the product to its final form, and such reaction to the final stage is accomplished without rigid backing forms, molds, the nal setting being attended with no warping or distortion of the fabric carrying the binder.

As a further embodiment of our invention it is contemplated by us to preliminarily heat the drying oil with the drier, short of forming a solid product and then incorporate the proportion of the phenolic-aldehyde resin, preferably the potentially reactive type, incorporate this mixture with the necessary quantity of thinner and then surface apply this mixture to the backing ma-- terial, in accordance with the sandpaper making processes ,previously described. It is preferred under such conditions, to substitute the phenolicresinous composition for only part of the resinous constituents specified in said Okie patents, and where a non-oil soluble phenolic resin is used, preferably preliminarily fusing the resinous constituents which may be used with the phenolic aldehyde resin, before incorporation into the vegetable fatty oil used.

In the embodiment above referred to, we have referred to the use of a phenol aldehyde condensation resin of the Bakelite type which is acetone and oil soluble and/or reactive with fatty oils, as the most suitable form of the resin which may be substituted in whole or in part for the resinous constituents in the formulae referred to, of the Okie patents.

The resinous material may be substituted in whole or in part in the Okie formulae heretofore referred to and comprising 12 to 39% oi resinous materials: fatty oil from 81 to 50%: driers from .5 to.1-% and the balance up to 40% of volatile thinner.

In distinguishing our foregoing form of `acetone and oil soluble and/or fatty oil vreactive resin which we may use. reference will be made to the'resin last described, which isa convenient one for our purposes, as the fphenol-fatty-oilreactive resin, which is so termed kby clear evidence of reaction, which takes place when this resin is heated with the fatty oil'hereinbelow described in the further production of the binder material, as distinguished from mere increase in body of the mixture with other resinous materials, notwithstanding polymerization of the fatty oil itself.

As another embodiment of an acetone and oilsoluble and/or fatty-oil-reactive resin whichwe may use yas the phenol-fatty-oil-reactive.resin" for purposes of reacting with afatty oil, in accordance with the prior procedure, the resinous condensation product of oil-soluble characteristics and reactive with oil in accordance'with the procedure previouslyoutllned, is a phenolic .aldehyde resin, or a` phenolic resinouscondensation product, in which the phenolic' constituent is either partially or completely an 'alkylxsubstituged phenol. The higher alkyl substituted phenol may be used and para tertiary'amyl or butyl phenol are given as examples.

In the preparation of the oil-soluble'andlor oil-reactive resinous material, utilizingthe` alkyl substituted phenol, these ingredients may be substituted for the phenol. Where 'the reacton'is with an aldehyde, it is convenient to reacty the alkyl substituted phenols and aldehydesin equal mol ratios with the usual condensingagents.

ln the furtherproduction of thebinder material of the Waterproofing composition, for our purposes, the phenol-fatty-oil-reactive resin just described is mixed with the proportionof fatty oil and drier, and heated in Yaccordance with the process heretofore described, at` a tern-` perature of .about 225 to 250 degrees C. 'I'l'iereafter, the percentage of thinner -is added.

While we have referred to substitution in whole or in .part of the phenol-aldehyderesin for the resinous component in the vformulae outlined and included by the Okie patents, where we use the resinous material hereinbefore referred to as the phenol-'fatty-oil-reactive .resin`,. it is preferred by `us to have this resinous constituent entirely replace the resinous constituentof the Okie formulae previously referredto. In making such complete substitution for theresinous material and after reaction as described and formation of they oil-resin complex in the volatile thinner, the solution of the polymerized oil andv phenol-fatty-oil-reactive resin" may vbe used for the making coat, binder coat :or sizing coat in the production of atough'and flexible abrasive article, with greater speedrof production than heretofore known, and twhere this complex of polymerized oil and phenol-fattyoil-reactive resin" is used, the-productnot only retains a homogeneous mixture through all stages of separation of the thinner,.but also. forced drying of high order may be practiced, without fear of segregation of vany-.portion of the resinousr constituents. After elimination of the thinner, the web and coating or coatings thus formed are submitted to air-drying action,..pref erably at elevated temperatures of 120 to 18B degrees as heretofore described.

The "phenol-fatty-oil-reactive resin and oil will react in all proportions of resin to oil, and hardness of the :dually reacted mixture may be increased with the increase of the "phenol-fattyoil-reactive resin. The increase in hardness is more abrupt up to the point of three parts of oil to one part of resin. As the proportion of .resin to oil is increased beyond this point, the increase in hardness is more gradual. At approximately the ratio of three parts of oil to one part of resin, the reacted mass shows substantially @greater toughness and greater hardness than the same `quantity of resin in an unreacted form. This serves not only as a basis for evidence of reaction of the resin and the oil, but also as a guide to alteration of the properties of the lnal proiduct with the variations of the ratio of oil to res n.

In the convenient practice immediately above referred to, wherein the phenol-fatty-oil-reactive resin" is completely substituted for the resinous constituents of the Okie formulae, thereby `completely eliminating the natural resins, any

tendency towards segregation of the resinous materials is completely avoided in all stages of separation of the volatile thinner or relative speeds of separation of said thinner, resulting in an exceedingly homogeneous end product of ascertainable uniformity without the retention of considerable saponiable constituents, and therefore rendering the product more adhesivein the presence of .abrasive particles, and in general, giving a product of greater waterproofness; greater hardness to resist displacement of such particles, or penetration of the binder by abraded particles, and greater toughness to permit higher speed vabrading operations.

As hereinabove pointed out, a convenient form of our binder or adhesive material may comprise substantially two and one half to three parts of China-wood oil to one part of phenol-fatty-oilreactive resin. This substance is highly waterproof yand forms a very strong, tough bond of good flexibility and a fair degree of stretch.

`For some purposes we have found the stress of stretch or distensibility of this binder to be somewhat too great, particularly where paper is used :as a backing material in an abrasive article `which is used in water abrading operations.

Thestress of stretch cr distensibiiity of the ybinder coat being greater than that of the moist paper Ybacking may cause the latter to develop vcracks while the abrasive article is in use, thus putting l the entire stress of the abrasive operationv of the binder coating, and thus reduce the useful life `of the abrasive article.

Y portions.

We ,have found that this diculty may .be overcome by adding a quantity of glyptal type of resin tothe resin-fatty-oil compound hereinbefore described. While some of the glyptal resins are not without some modification, as desirable for-our purposes as others herein particularly described, we have found that any glyptal resin which is miscible with fatty oils or oil varnishes, andpa'rticuiarly those which include the fatty acids of drying oils or semi-drying oils, obtains the desirable results when used in the proper pro- Forms of the glyptal resins referred to and which may be characterized as artificial rsins of the condensed ester type of polyhydric alcohols and resinifying carboxylic o'rganic acids or their anhydrides which are preferred for our purposes, may be produced as follows:

Example A 92 parts (by weight) of glycerine are heated with 148 parts of phthalic anhydride 'until' the evolution of gas decreases slightly, then -141 parts .of vegetable fatty acids (such as the fatty acid cordance with the application of Guth, Serial No.

347,159, entitled Flexible sheeted abrasive and method of making the same, and assigned 'to the Minnesota Mining and Manufacturing Company, may be utilized by us in accordance with the present invention. Thus, the glyptal resin may be made from polyhydric compounds of the character disclosed in said application, together with aromatic or cyclic polybasic acids, and though the phthalic anhydride may be used as a single aromatic acid, this may be substituted in whole y or combined with an aliphatic acid, such as oleic, butyric, succinic, citric, also benzoic, maleic,.glu taric, suberic, camphoric, adpic, linelic, eleostearic, lineoleic, linolenic. The acids above listed derived from drying oils are preferred by us and the lineleic, linelic, linolenic and eleostearic acids of the group enumerated are characteristic of acids derived from drying oi1s. which are so preferred.

Where still greater and adipic acids may be included as the resinifying carboxylic, organic acids, in addition'to the drying Aoil fatty acid above enumerated, and as partial or entire replacement for the phthalic anhydride in the example above given.

As a variation for the production.;.0f an-oil miscible or oil soluble glyptal type resin,l the following may be given:

Example B l Parts Glycerine 92 Phthalic anhydride 296 These ingredients are heated to 160 degrees-C., after which there is added 74 parts of phthalic anhydride and 140 parts of a fatty acid derived from a drying oil, such as China-wood oil, lin-- seed oil, perilla oil. These constituentsl are heated from 190-210 degrees C. until evolution of the gas decreases and resinification has been effected,

As a variation in the production of an oil-soluble glyptal type resin, which is Compatible to the oil contemplated in accordance with` our invention, as well as to the "phenol-fatty-oil-reactiveresin, for the purposes above numerated in con-v nection with forming the binder coat,.or for-a separate and distinct coat compatible with the phenolfatty-oil-reactive-resin China-wood oil binder coat, the following example -may be given.:

Example C v Parts Phthalic anhydride 4370 Drying oil fatty acid 140 These are heated to 160 degrees C. Thereupon 92 parts of glycerine are added and heated to 200 degrees C. to resinication.

Another example of a glyptal type of resin which we have found valuable for reducing the stress of stretch of the binder as described, par- This composition is thenVV flexibility is desired, suberic.

I rial lfor lan abrasive article, as an admixture with the ,"fatty-oil-reactive-resin andfatty-ioil com- '1oo'u1'1'd,"o`1" as a-separate compatible coating formingv the sizing for the paper backing or as a sand size yfor the grit bonded coating, a complex or `blend loffarglyptal resin and China-wood oil may be preparedias follows:

. y Erramplcv D Afglycerol phthalic anhydride resin and Chinawood oil in the proportionsl of equal parts of the resin andoil are dispersed in a high boiling solyvent, such as benzyl benzoate. The mixture is yheated to 10G-110 degrees C; until the China-Wood .'Ihesolvent is removed by precipitating the resin in anon-solvent for the resin. In this example,

other oils than China-wood oil may be used, such as linseed oil, perilla oil, soya bean oil, castor oil,

cottomseed oil. Other high boiling dispersing ,agents may be used and the glyptal resin may be used in Vits initial resinied stage.

We may also use an artificial resin complex of l. the condensed ester type and plienol-aldehyde process..

' Glycerol phthalic anhydride resin may be renl'dered compatible for the purposes contemplated Aby us by procedure avoiding the use of dispersing ,agents1 by a procedure which involves heating a mixtureof drying oil and resin inthe presence of a high-boiling... solvent. At a temperature of ,about 200 degrees C. the materials are thoroughly dispersed inthe solvent. It may then be mixed y with'a glycerolvphthalic anhydridev resin without the use o f a dispersing agent and in this form may AAbe used as an addition to the phenol-fatty-oilreactive-resinand fatty-oil compound for reducing the stress of stretch and for the purposes `contemplated by us as previously described. in

forming a coating compatible with the phenolfv'att'y-oilgreactive-resin" and fatty-oil compound which may beused.

l As an additional example of a phenol-aldehy'de glyptal type of resin which may be made for the purposes contemplatedby us, the following example may be given:

Example E 1A' phenol, preferably cresylic vacid and an aldevhyde, preferably paraldehyde, in equal molecular proportions, are .heated until a primary condensation is obtained. After purification to remove the-unrea'cted cresol, there is added 45 parts of phthalic anhydride;

. Parts Glycerol e 22 Linseedoil acids 23 phenol-aldehyde, cresci-furfural, phenol-ketone types of resins or resin forming ingredients.

As an additional form of oil soluble resin of the glyptal type, which may be used in association with the fatty oil reactive resin and fatty oil compound for the purposes indicated, this may be one resulting from forming a phenol type of resin in the presence of a natural esteriflable resin, the natural resin being esteriiied and the glyptal type resin being formed in the presence of the phenol resin esterifled natural resin mixture. The foilowing procedure may be employed Example F t Parts Rosin 250 Cresol 25 Paraformaldehyde 8 These ingredients are fiuxed successively at 100-125 degrees C. and 220 to 250 degrees C.

25 parts of an esterifying ingredient, such as glycerine, is added and heated to cause esterification by heating to 275 degrees C. Additional quantities of a polybasic acid. such as phthalic anhydride and glycerine are added and then heated, preferably in an atmosphere of carbon dioxide, at 200 to 240 degrees C., to form the glyptal type resin in the presence of the phenolresin esteried natural resin mixture.

As a still further example for the production of a compatible resin having glyptal resin characteristics, for the purposes contemplated by us, the following additional example may be given:

Example G Phthalic anhydride is reacted with an excess of glycerine until the evolution of the water vapor ceases. Thereupon, there is added a quantity of a drying oil fatty acid, such as linseed oil fatty acid, to react With the excess glycerine and the mixture heated until the desired consistency is obtained. The resulting resin may be further reacted with a phenol type of resin, which is oil soluble, which promotes the solubility of the mixture.

As a still further embodiment for the production of an alkyd for glyptal type of resin, compatible for the purposes herein'before described,

`the kfollowing additional example may be given:

Example H Parts Glycerine 180 Drying oil acid 280 The above ingredients are heated to a. temperature of 200 degrees C., for approximately one hour. "Io the mass so heated, there is added:

Parts Phthalic anhydride 290 alkyd or glyptal type resin may be made as follows:

Example I Parts Phthalic anhydride 70 Linseed oil acid or other drying oil acids 44 Glycerine 35 Coumarone resin 40 The above ingredients are heated at a ternperature of 250 degrees C. for approximately two and a half hours, after the temperature stated has been attained.

The foregoing procedure may be varied to the extent that after forming the resin from the phthalic anhydride, glycerine and drying oil fatty acid, as described, the oil soluble phenol type of resin that may be used is that which is hereinabove described as the phenol-fatty-oilreactive-resin.

In the examples enumerated under A to G, though we have described articial resins of the condensed ester type, which include in addition to the polyhydric alcohols, resinifying carboxylic organic acids or their anhydrides, preferring such resinifying carboxylic organic acids, in certain instances, such acids may be replaced, in whole or in part, by a synthetic resin carboxylic acid obtained by causing chloracetic acid to re act with the initial condensation product o! phenol and formaldehyde.

For purposes of simplifying the designation of the foregoingresinous mixtures, as enumerated under Examples A to I and the variations in procedure outlined thereunder, reference will be ing a backing material of paper in the formationof an abrasive article, and while We are not prepared to state exactly the physical or chemical function which the oil compatible glyptal resin performs in our composition, such addition, in effect, reduces the stress of stretch and renders the binder more retentive of its exibility. We obtain the desired degree of stretch and flexibility in the nished binder by adding an oil compatible glyptal resin to an extent of approximately 3 to 35%, preferably 10% of the "phenolfatty-oil-reactive-resin" and fatty oil compound.

While We may blend the "oil compatible glyptal resin with the "phenol fatty oil reactive resin or the China-Wood oil compound, or the mixture of the "phenol fatty oil reactive resin and China-wood oil compound, before polymerizing the phenolfatty-oil-reactive-resin and Chinawood oil compound, we prefer to first polymerize the phenol-fattymil-reactlve-resin and Chinawood oil to obtain the reaction or polymerization at the temperature of about 225 to 250 degrees C., and after reaction or polymerization and while the temperature is still approximately 235 degrecs C., the oil compatible glyptal resin is added. Thereafter the mass is permitted to cool and the necessary thinner is added. The oil compatible glyptal resins particularly those enumerated under Examples A to G, which include a phenolic constituent, may serve completely to displace the phenol-fattyoilreac tive-resin hereinbei'ore specifically described, in which embodiment the oil compatible glyptal resin and the China-wood oil or similar drying oil is reacted or polymerized, preferably in con- Junction with an agent to induce polymerization ,or reaction. Sum complex or "oil compatible glyptal resin" and oil, when polymerized, in accordance with thi'. procedure, provides a product which, though including the fatty oil in percentages of 50-81270 of the total mass, produces a film which dries rapidly.

The binder compound described abovel which includes the fatty-oil-reactive-resin, drying oil and oii compatible glyptal resin," ls particularly suitabl :.1 as a coating for the lighter grades oi' paper, that is, those. running from 40 to 50 pounds per ream, when this paper is used as a backing material in the preparation of sand- Papel'- For the purpose of illustrating the constructional features of the character above referred to and others contemplated by our invention, reference will be made to the accompanying drawing in which Figures 1-5 are sectional views through sandpaper, showing the backing and attached layers.

The embodiment illustrated in Figure 1 is preferably that construction previously referred to in making lighter grades of sandpaper. In this view a sheet 5 of relatively light paper is provided With a coating 6, comprising the binder herelnbei'ore described and which contains a quantity of the glyptal resin. The coating so provided penetrates partly to the backing, as shown at 1, and into this binder coating 6, while still plastic,there is provided a grit layer 8 of abrasive particles. l

Where heavier grades of paper are used, good results are obtained by applying a glyptal resin, such as Rezyl 1103, directly to the paper as a. presizing, though this presizing coat may be any other oi' the aforementioned oil compatible glyptal resins. When this coating is formed and partially or completely set, there Ais applied the binder coat comprising the phenol-fatty-oil-reactive-resin China-wood oil reacted composition. During the maturing of the binder coat,

sufficient interfusion takes place between the glyptal resin sizing coat and the binder coat so that the finished bond is strong and tough, and

possesses the proper degree of stretch to prevent cracking or breaking up of either the paper backing or the binder coat, particularly during rigorous liquid abrading operations.

In Figure 2, the paper sheeting I 0 of a relatively heavy grade is given a presizing coating II oi' the glyptal resin, such as Rezyl 1103 or any other oil compatible glyptal resin" hereinbefore described. This coating partially penetrates the backing I0 in the manner shown at I2. After partially or completely setting this sizing coat II, we overlie over the sizing coat a binder coat I3 and grit It. The coating I3 is preferably a "phenol-fatty-oil-reactive-resin and oil composition treated in accordance with the process heretofore described and penetrates and/or merges or homogenizes with the pre-sizing coat II, as shown at I5.

While the provision of an oil compatible glyptal resin" as a sizing coat in connection with a binder coat I3 of "phenol-fatty-oil-reactiveresin and oil is the preferred form, for the heavier grades of abrasive material, the inclusion in the binder coat composition I3 of small amounts of oil compatible glyptal resins blended therewith, also forms an exceedingly desirable binder coat composition.

In Figure 3 we have illustrated a variation in construction for forming the various layers of abrasives in the nature oi' sandpaper of the character illustrated in Figure 1 but with an additional application oi' a sand-sizing layer 9. In this embodiment, the binder layer 8 may coinprise the mixed complex of phenol-fatty-oil-reactive-resin" and China-wood oil reacted composition containing a quantity of oil compatible glyptal resins and when so using s uch binding layer, the sand sizing layer 9 may comprise a coating of a "phenol-fatty-oil-reactiveresin -China-wood oil reacted composition.

In still another embodiment of our invention. as illustrated in Figure 4, the backing material I6 may be provided with-a pre-sizing coat I1, overfwhich there is applied a binder coat I8 for holding the abrasive particles I9. 'I'he back sizing coat 28 may be applied to the opposite surface of the backing material. this construction, the binder coat I8 may comprise oil reactive resin and fatty oil reacted composition, with or without reacted oil compatible glyptal resins. The pre-sizing coat I1 is preferably an oil compatible glyptal resin, and for purposes oi' compensating for any distortion and otherwise improving the back surface of the paper, the back size 20 may also be formed of a coating of the same material as the presizing coat. Where the binder coat I8 comprises essentially an oil reactive resin and fatty oil reacted composition, the back sizing 20 may also be made of a coating of this same composition.

In Figure 5 there is illustrated a sectional view through sandpaper, essentially the same as in Figure 4, except that there is additionally applied a sand sizing coat 2i. Where the binder coat is essentially an oil reactive resin and fatty oil reacted composition, an oil compatible glyptal resin coating may constitute the sand sizing coating 2|. Preferably, however, the sand sizing coating 2I constitutes an oil reactive resin-fatty oil reacted composition, where the binder coat I8 includes an oil reactive resin and fatty oil reacted composition together with an oil compatible glyptal resin, or is essentially an oil compatible glyptal resin which, under certain circumstances, may entirely constitute the binder coat I8.

This application is a continuation-impart of our prior led application Serial No. 660,319, tiled March 10, 1933.

Having thus described our invention and illustrated its use what we claim as new and desire to secure by Letters Patent is:

l. A flexible abrasive article comprising a backing sheet and abrasive particles bonded thereto, the bond comprising a blend of a heatconvertible synthetic resin and a volatile organic solvent solution of a nlm-forming thermoplastic resin which is compatible with said heat-convertible synthetic resin, the said blend being reacted and polymerized to a hardened flexible state.

2. An abrasive article comprising a sheeted backing and abrasive particles bonded thereto, the bond comprising a blend of a heat-convertible phenol-aldehyde type resin and a volatile organic solvent solution of a thermoplastic resin which is compatible with said phenol-aldehyde type resin, the said blend being reacted and polymerized to a hardened flexible state.

3. A flexible-backed abradant especially adapted for wet sanding operations comprising a exible base coated with particles of abrasive imbedded in a water-resisting resinous composition which is the hardened homogeneous product resulting from reacting drying-oil-rnodied alkyd resin with a lesser but substantial proportion of phenol-aldehyde resin atan elevated temperature to a predetermined cure point.

4. A flexible-backed abradant comprising a flexible base, a hardened. water-resistant coating thereon consisting of a homogeneous product resulting from digestion under heat, to a predetermined cure point, a phenol-aldehyde type resin and a preponderant proportion of the product of reaction of a polyhydric alcohol, a polybasic carboxylic acid and a drying oil, and particles of abrasive material imbedded in s'aid coatmg.

5. A exible-backed abradant, comprising a flexible sheet material, a hardened, water-resistant coating thereon consisting of a homogeneous product resulting from reacting under heat glycerol, a polybasic carboxylic acid, and a reactant compound having the linseed cil acid radicals in the presence of phenol-aldehyde type resin in an amount less than one-half by weight of the whole, said reaction vbeing carried out at an elevated temperature to a predetermined cure point, and particles of abrasive material imbedded in said coating.

6. A flexible-backed abradant comprising a -fibrous sheet material, a hardened, water-resistant coating thereon consisting of a homogeneous product resulting from digesting under heat, to a predetermined cure point, phenol-aldehyde type resin and a preponderant proportion by Weight of the whole of the oil-modified alkyd resin product of reaction of a polyhydric alcohol, a

,polybasic carboxylic acid, and a compound having the perilla oil acid radicals, and particles of abrasive material imbedded in said coating.v

7. A flexible-backed abradant particularly adaptedv for wet sanding operations comprising a exible backing coated with particles of abrasive carried in a water-resistant resinous compo- 'sition which is the homogeneous product obtained by reaction under heat, to a predetermined cure point, of glycerol, phthalic anhydride, a compound having the linseed oil acid radicals, and phenol-aldehyde resin, the proportion of alkyd resin in the combined mass predominating over the proportion of phenol-aldehyde resin.

8. A ilexible-backed abradant especially adapted for wet sanding operations comprising a nexible base coated with particles of abrasive imbedded in a Water-resisting resinous composition which is the hardened homogeneous product resulting from reacting drying-oil-modifled. alkyd resin with a lesser but substantial proportion of a substituted phenol-aldehyde resin at an elevated temperature to a predetermined cure point, said substituted phenol being a phenol which is .substituted in the para position to the hydroxyl group by an alkyl radical having at least four carbon atoms.

9. A flexible-backed abradant comprising paper, a hardened, water-resistant coating thereon consisting of a homogeneous product resulting from digesting under heat, to a predetermined cure point, the reaction product of para-formaldehyde and a methyl substituted phenol with a preponderant proportion of the oil-niodied alkyd resin reaction product of glycerol, phthalic anhydride, and a compound having a drying oil acid radical, and particles of abrasive material imbedded in said coating.

10. A flexible backed abradant particularly adapted for Wet sanding operations comprising a flexible supporting medium coated with particles of abrasive material imbedded in a water-resisting resinous composition which is the hardened homogeneous product resulting from reacting a drying-oil-modified alkyd resin with a phenolaldehyde resin at an elevated temperature to a predetermined cure point, said alkyd resin being present in proportion by weight approximately equal to or greater than that of said phenol-aldehyde resin and the drying oil content of said composition being greater in weight than said phenol-aldehyde resin but not more than 21/2 times that of said phenol-aldehyde resin.

l1. A flexible-backed abradant especially adapted for wet sanding operations comprising a exible sheet material coated with particles of abrasive material carried in a hardened, water-resistant resinous composition which is the homogeneous product resulting from heating a liquid resinous composition comprising a volatile solvent and the product of reacting phenol-aldehyde resin material, glycerol, phthalic anhydride, and a reactant containing the linseed oil acid radicals.' the combined weight of the said glycerol and phthalic anhydride being greater than that of said phenol-aldehyde resin, and said reactant containing the linseed oil acid radicals being present by weight in greater proportion than said phenol-aldehyde resin but in lesser proportion than the combined weight of said glycerol, phthalic anhydride and phenol-aldehyde resin.

12. An abrasive article of the coated abrasive type comprising'a flexible backing coated with particles of abrasive embedded in a water-resisting resinous composition which is the hardened uniform product resulting from reacting an oilcompatible alkyd resin with a lesser but substantial proportion of a phenol-aldehyde type resin at an elevated temperature to a predetermined cure point, said alkyd resin comprising a polyhydric alcohol and a polybasic acid including maleic acid.

13. An abrasive article of the coated abrasiveV type comprising a backing sheet and abrasiveV grains bonded to said backing sheet by a plurality of coatings, one of said coatings being a presize or impregnating coat for said .backing sheet and comprising an oil-modied alkyd resin,

and another of said coatings being a grit bonding or binder coat and comprising the polymerization product of an oil reactive phenol-aldehyde resin and a drying oil.

14. An abrasive article ofthe coated abrasive type comprising a backing sheet and abrasive,

grains bonded to said backing sheet by a piurality of coatings, one of said coatings being a presize or impregnating coat for said backing sheet and comprising an oil-modified alkyd resin, and another of said coatings being a grit bonding or binder coat and comprising a weather-resisting resinouscomposition which is the hardcned homogeneous product resulting from reacting drying cil modied .alkyd resin with a lesser but substantial proportion of phenol-aldehyde resin at an elevated temperature to a predetermined cure point.

l5. An abrasive article of the coated abrasive type comprising a backing sheet and a plurality of adhesive coatings bonded thereto, one of said coating being` a presize or impregnating coat or said backing sheet and comprising a soft elastic waterproof resin varnish and another of said coatings being a grit-bonding or binder coat comprising an alkyd resin which is the hardened exible esteriflcation product of a polyhydric 

